This invention relates to improvements in pallet conveyor production line systems including pallets that have support members that are adjustable for carrying workpieces of different dimensions, and particularly to a pallet that is adapted to carry different sized workpieces and apparatus and methods for the automatic adjustment of the distance between support members of such pallets.
Pallet conveyor systems are used in automatic production lines where workpieces are to be subjected to a sequence of operations at successive workstations. A workpiece that is to be assembled, machined, or operated on is placed on support members that are mounted on a pallet. The pallet is set upon a moving conveyor belt that will advance the pallet and the workpiece to a series of workstations that perform the sequence of desired operations to complete the production cycle. A plurality of pallets carrying a like plurality of workpieces are typically used.
The pallets are frictionally driven by the conveyor. As a workpiece is brought to a workstation, the pallet is stopped and the workstation operation is performed. While stopped, the pallet may continue to rest on the moving conveyor in sliding contact, or may be lifted off the moving conveyor belt. Depending on the desired operation, the workpiece may be worked upon while resting on the support members of the pallet, or it may be removed from the support members, worked upon, and then returned to the support members. At the conclusion of the operation, the pallet is released or placed back on the belt to advance to the next workstation. The pallets thus move asynchronously, i.e., pallets upstream of a stopped pallet will advance until they are stopped behind a stopped pallet while the conveyor continues to advance, individually or in sets or groups, and accumulate in order to wait their turn at the workstation. Alternately, the pallets may move synchronously with respect to one another.
Pallet conveyor production lines are adapted for performing the same operations on workpieces that belong to the same family of workpieces and require the same machining operations, even though the workpieces may differ in certain dimensions. It is known to provide the workstations with automatic adjustment devices that can receive workpieces of different dimensions and adjust for the differences in order to perform properly the desired operation. However, to maximize efficiency of production, workpieces are usually grouped and processed in sets according to the uniformity of certain dimensions. This minimizes the amount of changing-time and thus increases the rate of through-put of finished parts.
One of the problems with conventional pallet conveyor systems is that the support members on the pallets are manually adjusted for the dimensions of the particular workpieces for the production cycle. Conventional pallets have mechanical connecting links or fasteners that must be manually loosened so that the support members can be moved, and then refastened to secure the workpiece support members to the pallet in the proper location to support a workpiece. Thus, to change production from a set of workpieces having one uniform dimension to another, either the pallets must be adjusted while the pallets are advancing on the conveyor line or while pulled off the conveyor line. Alternately, the pallets may be replaced with a second set of pallets that are pre-adjusted for the dimensions of the next set of workpieces. Consequently, changing from one set of workpieces to another requires a significant slowdown or down-time in production.
Another problem with conventional production lines is that the manual adjustment procedure allows for error in the settings used from one pallet to the next. Consequently, the workpieces are not always properly or uniformly carried during the production cycle, which may result in differences in the quality of the finished products.